Optimization system and optimization method for absorber coating of solar thermal power system

Abstract

The present invention provides an optimization system and method for a solar thermal power system absorber coating, and the optimization method includes the following steps: S1: obtaining the energy flux density distribution on the absorber surface; S2: obtaining the absorber temperature distribution under the energy flux density; S3: adjusting the coating coverage strategy of the over-temperature area on the absorber surface according to the absorber temperature distribution to reduce the optical absorption rate of the over-temperature area; S4: obtaining the corresponding absorber temperature distribution under the energy flux density after adjusting the coating coverage strategy; S5: repeating steps S3 and S4 until the absorber temperature distribution is within the specified absorber temperature range. The present invention has low requirements on the control system accuracy of the heliostat, does not consume a large amount of computing resources to increase additional system costs, can make the temperature distribution of the heat receiving surface of the absorber uniform under the premise of ensuring that the energy received by the absorber is as much as possible, avoids excessive local temperature of the absorber, is conducive to protecting the absorber, improving heat exchange efficiency, and enhancing system performance.

Description

Technical Field

[0001] The present invention relates to the field of solar energy technology, and in particular to an optimization system and an optimization method for a solar thermal power system absorber coating. Background Art

[0002] Energy has promoted the production progress and economic prosperity of human society. The vigorous development and use of coal, oil, natural gas, etc. have led to abnormal global climate change and increasingly serious environmental pollution. Accelerating the development of renewable energy technology is an important direction for adjusting the energy structure. Solar energy is an inexhaustible and best renewable energy source that is available all over the world. The development and utilization of solar energy, a clean and pollution-free renewable energy source, is of great significance to reducing the current pressure of fossil energy and environmental pollution.

[0003] There are four main types of existing solar thermal power generation technologies, namely tower solar thermal power generation, trough solar thermal power generation, linear Fresnel solar thermal power generation and dish solar thermal power generation. Among them, tower solar thermal power generation technology can effectively improve the overall efficiency of solar thermal power stations due to its high concentration ratio and high operating temperature. It is a solar thermal power generation technology with great application prospects.

[0004] The absorber is a key device for converting light energy into heat energy in a tower solar thermal power station. During the operation of the power station, thousands of heliostats focus sunlight on the surface of the absorber to heat the working fluid in the absorber tube. Usually, a layer of coating material is applied to the surface of the absorber tube to enhance the absorber tube's absorption of sunlight and improve thermal efficiency. However, when the system is actually running, the distribution of solar energy flow focused on the absorber surface is non-uniform, which will cause uneven heating of the absorber tube and excessive local temperature, resulting in low heat exchange efficiency, excessive stress on the absorber tube, and even damage to the absorber, which in turn affects the reliability of the entire system. Therefore, a reasonable strategy must be adopted to optimize the temperature distribution of the absorber's heating surface. On the premise of ensuring that the absorber receives as much energy as possible, the temperature distribution of the absorber's heating surface should be more uniform, and high local temperatures and large temperature gradients should be avoided, so as to protect the absorber, facilitate heat exchange, and ensure the stability of the system.

[0005] Most of the existing studies on strategies for optimizing the temperature distribution on the surface of the heat sink focus on the aiming strategy of the heliostat field. By adjusting the pointing point of the heliostat, the energy flow distribution focused on the heat sink is changed to affect the temperature distribution. However, these heliostat strategies will reduce the input energy of the heat sink and place high demands on the accuracy of the heliostat. Especially for large-scale mirror fields, the cost of the heliostat control system increases and a large amount of computing resources are consumed. Therefore, a simpler and more effective strategy is needed to optimize the temperature distribution on the surface of the heat sink. Summary of the invention

[0006] In view of the above problems, the present invention provides an optimization system and method for the absorber coating of a solar thermal power system, which can make the temperature distribution of the heated surface of the absorber uniform while ensuring that the absorber receives as much energy as possible, and has low requirements on the accuracy of the heliostat control system, and does not consume a large amount of computing resources to increase additional system costs.

[0007] In order to solve the above problems, the present invention provides a method for optimizing the coating of a solar thermal power system absorber, comprising the following steps:

[0008] S1: Obtain the energy flux density distribution on the absorber surface;

[0009] S2: Obtain the temperature distribution of the heat sink under the energy flux density;

[0010] S3: According to the temperature distribution of the absorber, the coating coverage strategy of the over-temperature area on the surface of the absorber is adjusted to reduce the optical absorption rate of the over-temperature area;

[0011] S4: obtaining the corresponding absorber temperature distribution under the energy flux density after adjusting the coating coverage strategy;

[0012] S5: Repeat steps S3 and S4 until the absorber temperature distribution is within the specified absorber temperature range.

[0013] The present invention has low requirements on the accuracy of the heliostat control system and does not consume a large amount of computing resources to increase additional system costs. It can ensure that the temperature distribution of the heated surface of the absorber is uniform while ensuring that the absorber receives as much energy as possible, thus avoiding excessive local temperature of the absorber. This is beneficial to protecting the absorber, improving heat exchange efficiency, and enhancing system performance, providing a reference for the operation of solar thermal power stations.

[0014] In an optional technical solution of the present invention, before step S1, it also includes step S0: focusing the heliostat to the absorber, and the focusing point of the heliostat is the geometric center of the absorber.

[0015] According to this technical solution, the energy flux density distribution and temperature distribution of the heat absorber's heating surface can be made more uniform while ensuring that the heat absorber receives as much energy as possible, avoiding the occurrence of high local temperatures and large temperature gradients, thereby protecting the heat absorber, facilitating heat exchange, and ensuring the stability of the system.

[0016] In an optional technical solution of the present invention, in step S1, a Monte Carlo ray tracing method is used to simulate the propagation process of light in the heliostat and the absorber, and the energy flux density distribution on the surface of the absorber is calculated.

[0017] According to this technical solution, by simulating the propagation process of light in the heliostat and the absorber, the calculated energy flux density distribution on the absorber surface is closer to the actual energy flux density distribution and has higher accuracy, thereby improving the accuracy of the energy flux density distribution on the absorber surface and further improving the accuracy of the temperature distribution on the absorber surface.

[0018] In the optional technical solution of the present invention, step S1 also includes: gridding the heating surface of the heat absorber, and at the time point when the DNI is the highest, for each heliostat, according to a method combining geometric projection and ray tracing, calculating the energy flux density value of each grid on the surface of the heat absorber at the time when the DNI is the highest, thereby obtaining the corresponding energy flux density distribution, and the calculation formula of the energy flux density value of each grid on the surface of the heat absorber is:

[0019]

[0020] In the formula, q is the energy flux density; e is the energy carried by each light ray; n is the number of light rays absorbed by the grid unit; A is the area of ​​the grid unit;

[0021] According to this technical solution, the energy flux density distribution on the surface of the absorber is closer to the actual energy flux density distribution, and the calculation speed and accuracy of the energy flux density are improved.

[0022] In an optional technical solution of the present invention, in step S2, the finite volume method is used to calculate the temperature distribution of the heat absorber using the energy flux density obtained in step S1 as the thermal boundary condition.

[0023] According to the technical solution, the finite volume method has the advantage of fast calculation speed and can reduce the consumption of a large amount of computing resources.

[0024] In an optional technical solution of the present invention, in step S3, adjusting the coating coverage strategy of the over-temperature area on the surface of the heat absorber includes: adjusting the optical absorption rate of the heat absorber by adjusting the thickness or color of the coating.

[0025] According to this technical solution, the coating coverage strategy is adjusted in a simple and easy way and by changing the coating coverage strategy, the temperature distribution on the surface of the absorber can be effectively changed, thereby avoiding local over-high temperatures and ensuring that the temperature of each area on the surface of the absorber is within the specified temperature range.

[0026] In an optional technical solution of the present invention, the heat absorber is a heat absorber using one of water, air, molten salt or supercritical carbon dioxide as a working fluid.

[0027] According to the technical solution, the coating optimization method of the present invention is applicable to a variety of different working fluids and different types of heat absorbers, has strong adaptability, and is suitable for popularization and use.

[0028] In an optional technical solution of the present invention, the heat absorber is a cavity heat absorber.

[0029] According to this technical solution, the energy not absorbed by the high-temperature area of ​​the cavity-type heat absorber will be reflected in the cavity and absorbed by the low-temperature area of ​​the heat absorber, thereby increasing the temperature of the low-temperature area and improving the optical absorption rate and energy utilization rate of the heat absorber.

[0030] The present invention further provides a solar thermal power system absorber coating optimization system, which executes the above-mentioned solar thermal power system absorber coating optimization method. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of a method for optimizing a solar thermal power system absorber coating in an embodiment of the present invention.

[0032] Figure 2 Schematic diagram of the structure of the heat absorber in an embodiment of the present invention.

[0033] Figure 3 Schematic diagram of coating coverage on the surface of the heat absorber tube before adjusting the coating coverage strategy in an embodiment of the present invention.

[0034] Figure 4 Schematic diagram of energy flux density distribution before adjusting the coating coverage strategy in an embodiment of the present invention.

[0035] Figure 5 Schematic diagram of the grid unit division of the surface of the heat absorption tube in an embodiment of the present invention.

[0036] Figure 6 Schematic diagram of temperature distribution before adjusting the coating coverage strategy in an embodiment of the present invention.

[0037] Figure 7 Schematic diagram of coating coverage on the surface of the heat absorber tube after adjusting the coating coverage strategy in an embodiment of the present invention.

[0038] Figure 8 Schematic diagram of temperature distribution after adjusting the coating coverage strategy in an embodiment of the present invention.

[0039] Reference numerals:

[0040] Cavity heat absorber 1; inlet header 11; outlet header 12; daylighting header 13; heat absorption pipe 14; thermal insulation layer 15. DETAILED DESCRIPTION

[0041] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0042] See also Figure 1 As shown, the present invention provides a method for optimizing a coating of a solar thermal power system absorber, comprising the following steps:

[0043] S1: Obtain the energy flux density distribution on the absorber surface;

[0044] S2: Obtain the temperature distribution of the heat sink under the energy flux density;

[0045] S3: According to the temperature distribution of the absorber, the coating coverage strategy of the over-temperature area on the surface of the absorber is adjusted to reduce the optical absorption rate of the over-temperature area;

[0046] S4: obtaining the corresponding absorber temperature distribution under the energy flux density after adjusting the coating coverage strategy;

[0047] S5: Repeat steps S3 and S4 until the absorber temperature distribution is within the specified absorber temperature range.

[0048] The present invention has low requirements on the accuracy of the heliostat control system and does not consume a large amount of computing resources to increase additional system costs. It can ensure that the temperature distribution of the heated surface of the absorber is uniform while ensuring that the absorber receives as much energy as possible, thus avoiding excessive local temperature of the absorber. This is beneficial to protecting the absorber, improving heat exchange efficiency, and enhancing system performance, providing a reference for the operation of solar thermal power stations.

[0049] In a preferred embodiment of the present invention, before step S1, the method further includes step S0: focusing the heliostat onto the heat absorber, wherein the focusing point of the heliostat is the geometric center of the heat absorber.

[0050] Through the above method, it is possible to ensure that the heat absorber receives as much energy as possible, while making the energy flux density distribution and temperature distribution of the heating surface of the heat absorber more uniform, avoiding the occurrence of high local temperatures and large temperature gradients, thereby protecting the heat absorber, facilitating heat exchange, and ensuring the stability of the system.

[0051] In a preferred embodiment of the present invention, the absorber is a cavity absorber 1. The energy not absorbed by the high temperature area of ​​the cavity absorber 1 will be reflected in the cavity and absorbed by the low temperature area of ​​the absorber, thereby increasing the temperature of the low temperature area, improving the optical absorption rate and energy utilization rate of the absorber. In step S0, the heliostat is focused on the light-collecting port of the absorber, and the focus point is selected as the geometric center of the light-collecting port. Further, as Figure 2 As shown, the cavity heat absorber 1 includes an inlet header 11, an outlet header 12, a light-emitting port header 13, a heat absorption tube 14 and a thermal insulation layer 15. The structure of the cavity heat absorber 1 is a common application form in this field and will not be repeated here. Figure 3The figure shows the coating coverage schematic diagram of the heat absorber tube surface before adjusting the coating coverage strategy. Each heat absorber tube is coated evenly, and the area circled by the dotted line is the over-temperature area.

[0052] In a preferred embodiment of the present invention, in step S1, the Monte Carlo ray tracing method is used to simulate the propagation process of light in the heliostat and the absorber to calculate the energy flux density distribution on the surface of the absorber.

[0053] In the above manner, by simulating the propagation process of light in the heliostat and the absorber, the calculated energy flux density distribution on the absorber surface is closer to the actual energy flux density distribution and has higher accuracy, thereby improving the accuracy of the energy flux density distribution on the absorber surface, thereby improving the accuracy of the temperature distribution on the absorber surface.

[0054] In a preferred embodiment of the present invention, step S1 further includes: gridding the heating surface of the heat absorber, and at the time point when DNI (Direct Normal Irradiance) is the highest, for each heliostat, calculating the energy flux density value of each grid on the surface of the heat absorber at the time when DNI is the highest according to a method combining geometric projection and ray tracing, thereby obtaining the corresponding energy flux density distribution. The calculation formula of the energy flux density value of each grid on the surface of the heat absorber is shown in formula (1):

[0055]

[0056] In the formula, q is the energy flux density; e is the energy carried by each light ray; n is the number of light rays absorbed by the grid unit; A is the area of ​​the grid unit;

[0057] Through the above method, the energy flux density distribution on the surface of the absorber is closer to the actual energy flux density distribution, and the calculation speed and accuracy of the energy flux density are improved.

[0058] Specifically, the heated surface of the absorber is gridded to form (e.g., R x L) grids, where R is the number of circumferential grids and L is the number of radial grids. At the highest DNI time point, the energy flux density value of each grid focused on the heated surface of the absorber by a certain heliostat is calculated in MATLAB based on a method combining geometric projection and ray tracing, thereby obtaining the corresponding energy flux density matrix. Repeat this process until the energy flux density matrix generated by all heliostats is obtained. Adding the energy flux density matrices generated by all heliostats is the energy flux density matrix of the entire heliostat field on the heated surface of the absorber, which serves as the basis and foundation for the thermodynamic calculation of the absorber. In some other embodiments, other methods may also be used to calculate the energy flux density, and the present invention does not limit the method for obtaining the energy flux density. For example Figure 4The schematic diagram of energy flux density distribution before adjusting the coating coverage strategy in the embodiment of the present invention is shown. The energy flux distribution on the two side walls of the heat absorber (the position circled by the dotted rectangle in the figure) is the most concentrated, and the energy flux density value is relatively high.

[0059] In a preferred embodiment of the present invention, in step S2, the finite volume method is used to calculate the temperature distribution of the heat absorber using the energy flux density obtained in step S1 as the thermal boundary condition. The finite volume method has the advantage of fast calculation speed and can reduce the consumption of a large amount of computing resources.

[0060] Specifically, the heat absorber is composed of a heat absorber tube row, and the heat absorber tube row is composed of a heat absorber tube 14. After the calculation is completed, the highest temperature area in each heat absorber tube 14 of the heat absorber can be obtained; the finite volume method can be used to solve the temperature distribution of the heat absorber with the help of the commercial CFD software package FLUENT, or by self-programming; when FLUENT is used for calculation, the energy flux density distribution obtained in step S1 is imported into the finite volume method model through a user-defined equation, and the turbulence model adopts the standard k-ε model. When self-programming is used, the mesh division of the outer surface of the heat absorber tube 14 is consistent in step S1 and step S2, and the energy flux density distribution obtained in step S1 is directly assigned to the mesh in step S2.

[0061] For the FLUENT calculation method, this method obtains the flow heat transfer performance of the heat absorber by directly solving the Navier-Stokes equations. The calculation accuracy is high, but it also occupies more computing resources. This method can be used when computing resources are sufficient. For the self-programming method, the convective heat transfer of the heat transfer fluid in the heat absorber is solved by the flow heat transfer correlation. The computing resources are less. This method can be used when computing resources are scarce. If the accuracy of the convective heat transfer correlation used is high, this method can also obtain a more accurate temperature distribution.

[0062] In a specific embodiment of the present invention, a self-programming method is used to calculate the temperature distribution of the heat sink, such as Figure 5 As shown, the heat absorber 14 is divided into a light-facing surface, a fluid domain and a backlight surface. The energy balance equation of the light-facing surface is shown in equations (2), (3), (4) and (5). The energy balance equations of the fluid domain and the backlight surface can be calculated similarly. The grid division of the absorber surface is consistent with that in step S1. The energy flux density distribution obtained in step S1 is directly assigned to the grid in step S2. Using MATLAB programming, the temperature distribution diagram of the absorber is obtained, as shown in Figure 6In the temperature distribution diagram before adjusting the coating coverage strategy, the energy flow distribution on the walls on both sides of the heat absorption tube 14 is most concentrated (the dark area in the rectangular box in the figure, that is, the area with the highest temperature). Setting the low-temperature tube in the area with the most concentrated energy flow helps to reduce the maximum wall temperature of the heat absorption tube 14. However, even if the position of the low-temperature tube in the energy flow is adjusted, the maximum wall temperature is still 618°C.

[0063]

[0064]

[0065]

[0066] q in =q 1 +q 2 +q 3 (5)

[0067] In the formula, q in To receive energy for the light-facing side;

[0068] q 1 It is the heat conduction between the light-facing surface and the adjacent solid units;

[0069] q 2 Convective heat transfer between the light-facing surface and the working fluid;

[0070] q 3 Transfer heat conduction and heat exchange to the backlight side and light-facing side of the heat absorber;

[0071] λ is the thermal conductivity of the tube wall, W / m·K;

[0072] x is the axial distance between adjacent grid cells, in m;

[0073] h 2 is the forced convection heat transfer coefficient between the light-facing wall and the fluid, W / m 2 K, can be obtained by Gnielinski's formula;

[0074] l is the circumferential distance between the light-facing surface and the backlight surface unit, in meters;

[0075] T j，i , is the temperature of the grid at the axial position i in the j region of the heat absorber, j=1, 2, 3, j=1 represents the light-facing surface of the heat absorber tube 14, j=2 represents the fluid domain of the heat absorber tube 14, j=3 represents the backlight surface of the heat absorber tube 14, the unit is ℃; A1, A2, A3 represent the axial heat transfer areas at different positions, S1, S2, S3 correspond to the radial heat exchange areas at different positions, i-1, i+1 represent the positions of the grid units adjacent to i; q rad represents radiation heat transfer; q4 is the convective heat transfer between the backlight surface and the working medium, q 5 It is the heat conduction between the backlit surface and the adjacent solid units.

[0076] In a preferred embodiment of the present invention, in step S3, the coating coverage strategy for adjusting the over-temperature area on the surface of the heat absorber includes: adjusting the optical absorptivity of the heat absorber by adjusting the thickness or color of the coating. Furthermore, if there is still an over-temperature area, the optical absorptivity of the coating in the high-temperature area can be further reduced by changing the color or thickness of the coating, or the range of coating adjustment can be expanded. The coating coverage strategy of the present invention is simple to adjust and easy to operate, and by changing the coating coverage strategy, the temperature distribution on the surface of the heat absorber can be effectively changed without reducing the energy input of the heat absorber, thereby avoiding the occurrence of dangerous conditions caused by local over-high temperatures and ensuring that the temperature of each area on the surface of the heat absorber is within the specified temperature range. Figure 7 Schematic diagram of coating coverage on the surface of the heat absorber tube after adjusting the coating coverage strategy in an embodiment of the present invention. Figure 7 The portion corresponding to the over-temperature area is coated with a light-colored coating to reduce the optical absorption rate and the temperature of the area. The other areas of the heat absorbing tube 14 are normally coated to ensure a high energy utilization rate. Figure 8 It can be seen that the area enclosed by the dotted rectangular box is the coating coverage strategy adjustment area. The maximum temperature in the coating coverage strategy adjustment area is 578°C. Compared with before adjusting the coating coverage strategy, the maximum temperature has dropped by 40°C, and the effect is significant.

[0077] The present invention does not add any additional equipment, only adjusts the coating brushing strategy on the surface of the absorber heat absorption tube 14, does not reduce the input energy of the absorber and does not have excessive requirements on the control system of the heliostat. It can effectively improve the performance of the absorber while ensuring the safe operation of the absorber, and contributes to the improvement of the overall efficiency of the solar thermal power system (such as the tower solar thermal power system).

[0078] In a preferred embodiment of the present invention, the working fluid of the heat absorber can be water, air, molten salt, supercritical carbon dioxide, etc. The coating optimization method of the present invention is applicable to a variety of heat absorbers with different working fluids and forms, has strong adaptability, and is suitable for popularization and use.

[0079] The present invention further provides a solar thermal power system absorber coating optimization system, which executes the above-mentioned solar thermal power system absorber coating optimization method.

[0080] The optimization system of the present invention has low requirements on the accuracy of the heliostat control system and does not consume a large amount of computing resources to increase additional system costs. It can ensure that the temperature distribution of the heated surface of the absorber is uniform while ensuring that the absorber receives as much energy as possible, thus avoiding excessive local temperature of the absorber. It is beneficial to protect the absorber, improve heat exchange efficiency, enhance system performance, and provide a reference for the operation of solar thermal power stations.

[0081] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for optimizing the coating of a solar thermal power system absorber. It is characterized in that The following steps are involved: S1: Obtaining the energy flux density distribution on the surface of the heat absorber, including gridding the heating surface of the heat absorber, and calculating the energy flux density value of each grid on the surface of the heat absorber for each heliostat at the time point of the highest DNI by combining geometric projection and ray tracing. The calculation formula of the energy flux density value is: q is the energy flux density, e is the energy carried by each ray, n is the number of rays absorbed by the grid unit, and A is the area of ​​the grid unit; S2: Using the finite volume method, taking the energy flux density obtained in step S1 as the boundary condition, the temperature distribution of the heat absorber under the energy flux density is obtained. The energy balance equation of the finite volume method includes the heat conduction relationship between the light-facing surface, the fluid domain and the backlight surface, which is specifically: q in =q 1 +q 2 +q 3 in, q in For the light-facing side to receive energy, q 1 is the heat conduction between the light-facing surface and the adjacent solid unit, q 2 is the convective heat transfer between the light-facing surface and the working fluid, q 3 is the heat transfer between the backlight side and the light-facing side of the heat absorber, λ is the thermal conductivity of the tube wall, x is the axial grid spacing, h 2 is the convective heat transfer coefficient, l is the circumferential grid spacing, T j,i is the temperature of different areas; S3: determining an over-temperature region according to the temperature distribution of the heat absorber, and adjusting a coating coverage strategy of the over-temperature region on the surface of the heat absorber to reduce an optical absorption rate of the over-temperature region; S4: After obtaining the coating coverage strategy, the corresponding heat sink temperature distribution under the energy flux density; S5: Repeat steps S3 and S4 until the heat absorber temperature distribution is within the specified heat absorber temperature range.

2. The method for optimizing the coating of the solar thermal power system absorber according to claim 1, It is characterized in that Before step S1, the method further includes step S0: focusing the heliostat onto the heat absorber, wherein the focusing point of the heliostat is the geometric center of the heat absorber.

3. The method for optimizing the coating of the solar thermal power system absorber according to claim 1, It is characterized in that In step S1, the Monte Carlo ray tracing method is used to simulate the propagation process of light in the heliostat and the absorber, and the energy flux density distribution on the surface of the absorber is calculated.

4. The method for optimizing the coating of the solar thermal power system absorber according to claim 1, It is characterized in that In step S3, adjusting the coating coverage strategy of the over-temperature area on the surface of the heat absorber includes: adjusting the optical absorption rate of the heat absorber by adjusting the thickness or color of the coating.

5. The method for optimizing the coating of the solar thermal power system absorber according to any one of claims 1 to 4, It is characterized in that The heat absorber is a heat absorber using one of water, air, molten salt or supercritical carbon dioxide as a working fluid.

6. The method for optimizing the coating of the solar thermal power system absorber according to claim 1, It is characterized in that The heat absorber is a cavity type heat absorber.

7. An optimization system for the absorber coating of a solar thermal power system, It is characterized in that A method for optimizing a solar thermal power system absorber coating according to any one of claims 1 to 6.

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